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This research provides a description of the epiphytic diatom community living on the blades of the marine seagrass Posidonia oceanica in the coastal area of the eastern Adriatic Sea. Samples were collected in May 2017, from a meadow located in Tetevišćica Bay, on the western side of Dugi otok island (43° 58’ 22’’ N; 15° 03’ 36’’ E) at three depths: 10, 15 and 20 m. Each blade sample was divided into three segments along the leaf axis (basal meristemal, middle and apical) to explore the possible community zonation pattern. Twenty-one samples were analyzed by light microscope and the epiphytic diatom community structure was determined. A total of 68 taxa belonging to 30 genera were found: 43 from 10 m depth, 41 from 15 m depth and 39 from 20 m depth. All identified species are commonly recorded from other marine benthic periphytic and epiphytic habitats. The genus Cocconeis was dominant in all samples, which is typical for epiphytic biofouling of P. oceanica leaves. Although no changes in the community structure related to the position on P. oceanica blade were observed, ANOSIM tests (p<0.05) performed on species’ relative abundances confirmed that the diatom communities differed significantly according to their depths. This study contributed to the knowledge on biodiversity associated with Adriatic P. oceanica meadows, which are threatened by human activities and invasive species. Additionally, this research provided important information on the identification of the taxa-specific epiphytic diatom community on seagrasses in the eastern Adriatic Sea., U ovom je radu istraživan epifitski obraštaj algi kremenjašica (dijatomeja) na listovima morske cvjetnice Posidonia oceanica u obalnom području istočnog Jadrana. Uzorci su sakupljeni u svibnju 2017, s livade morske cvjetnice u uvali Tetevišćica (43° 58’ 22’’ N; 15° 03’ 36’’ E) koja se nalazi na zapadnoj obali Dugog Otoka s ukupno tri dubine: 10, 15 i 20 m. Svaki uzorak lista podijeljen je duž lisne osi na tri dijela: bazalni, srednji te apikalni dio. Analiziran je 21 uzorak pomoću svjetlosnog mikroskopa te određena struktura epifitskih dijatomejskih zajednica. Identificirano je ukupno 68 svojti podijeljenih u 30 rodova, 43 svojte s dubine 10 m, 41 s dubine 15 m i 39 s dubine 20 m. Sve zabilježene svojte su tipične za morska bentička, perifitonska i epifitska staništa. Rod Cocconeis bio je dominantan u zajednicama na svim dubinama, što je i karakteristika epifitskih obraštaja na listovima P. oceanica. Unatoč tome što nije zabilježena razlika u zajednicama dijatomeja s obzirom na položaj na listu, ANOSIM test (p<0.05) na temelju relativne brojnosti vrsta potvrdio je da se zajednice dijatomeja značajno razlikuju između dubina. Ovo istraživanje doprinosi poznavanju bioraznolikosti jadranskih naselja P. oceanica koje su trenutno ugrožene ljudskim aktivnostima i širenjem invazivnih vrsta. Također, ovo je istraživanje važno za poznavanje zajednice epifitskih dijatomeja na morskim cvjetnicama u Jadranskom moru.